Regulations require passenger aircraft to carry a fire extinguisher. Some extinguishers are required to put out an EN34B fire in which the extinguisher must put out 34 liters of flammable liquid, for example heptane, before expiring. In the past, an aircraft might have carried extinguishers that used the various formulations of Halon that were effective but since deemed to be dangerous to the atmosphere.
Newer extinguishers use other fluids as a substitute for Halon. Such fluids are usually discharged as a stream of gas and liquid droplets that penetrate into the fire area and cause the combustion process to end through heat absorption and a chemical interaction.